This invention relates to an improved process for the preparation of a carboxylic acid. Particularly, this invention relates to an improved process for conversion of an olefin, organic halide or aryl alcohol to the corresponding saturated carboxylic acid.
Aryl and aliphatic carboxylic acids have a variety of applications in industries as anti-inflammatory drugs, fine chemicals, etc. The prior art describes catalyst systems for employment in processes for the preparation of carboxylic acids by the carbonylation of corresponding alcohols, olefins or halo derivatives. The best known of such catalysts are homogeneous palladium catalysts. In the processes described in literature, the catalysts used were mainly Pd(PPh3)2Cl2 or PdCl2 or Pd(OAc)2 along with excess phosphine ligands (EP 0,400,892A3, EP 0,284,310A1, U.S. Pat, No. 5,315,026, J. Mol. Catal., 1992, 77, 7-13, U.S. Pat. No. 5,260,477), which gave lower reactions rates (TOF=25-35 hxe2x88x921) under mild conditions (130xc2x0 C., 1000 psig). In the publications, Catalysis Letters 1999, 61, 1-2: 99-103 and Organic Letters, 1999, 1:1, 459-461, high reaction rates (TOF=up to 2600 hxe2x88x921) and 2-arylpropionic acid selectivity ( greater than 95%) was reported for the carbonylation of 1-arylethanols and vinyl aromatics using a catalyst system consisting of PdCl2(PPh3)2/TsOH/LiCl in a homogeneous medium under relatively mild reaction conditions (115xc2x0 C. and 800 psig). The U.S. Pat. No. 6093847 describes the carbonylation of 1-(4-isobutylphenyl)ethanol (IBPE) using novel Pd complexes having general formula V wherein Rxe2x80x21, Rxe2x80x22 and Rxe2x80x23 are substituents on the phosphine ligand such as, alkyl, aryl, arylalkyl, cycloaliphatic, X is groups such as aryl or alkyl sulfonato or aryl or alkyl carboxylate or formato or halides such as Clxe2x88x92, Brxe2x88x92, Ixe2x88x92, 
is an anionic chelating ligand containing a N donor and Oxe2x80x94 group such as 8-hydroxyquinoline, 2-hydroxypyridine, (2-hydroxyethyl)pyridine, pyridil-2-, pyrezyl-2, piperidyl-2-, piperzyl-2-, quinolyl-2-, isoquinolyl-1- and isoquinolyl-2- carboxylates, particularly pyridyl-2-carboxylate, piperidyl-2-carboxylate and 8-hydroxyquinoline, which also gave high reaction rates and Ibuprofen selectivity under similar conditions.
A major disadvantage of all these processes is the difficulty in separation of the catalyst from the product and its recycle. An important solution for this problem is the application of two-phase systems comprising an aqueous phase containing water-soluble organometallic catalysts and a water immiscible phase (U.S. 31812; CHEMTECH 17, 1987, 570; EP 0107006; Aqueous-Phase Organometallic Catalysis B. Cornils, W. A. Herrmann (Eds.),Wiley-VCH, 1998, Weinheim.). In this case, separation of the organometallic catalyst from organic reactants and products is greatly simplified due to the insolubility of the catalyst in water immiscible phase. The publications New. J. Chem, 1997, 21, 529-531, New. J. Chem, 1997, 21, 857-859 and Catal. Lett., 1997, 47, 43-46 revealed the carbonylation of olefins to carboxylic acids using a biphasic catalyst system (PdCl2/TPPTS) under 50 bar CO pressure at 65-100xc2x0 C. U.S. Pat. No. 5,536,874 and the publication, J. Chem. Tech. Biotechnol, 1997, 70, 83-91, describe the carbonylation of p-IBPE in a two-phase system wherein one phase is an aqueous medium which contains a water soluble palladium complex and an acid promoter. These processes allow easy separation of the catalyst from the product and its recycle, however, the reaction rates (TOF=0.1 to 50 hxe2x88x921) and 2-arylpropionic acid selectivity (59-74%) were very low under relatively mild reaction conditions (90xc2x0 C., 450 to 900 psig).
Therefore it is important to develop processes which use new and improved catalysts that give good yields of carboxylic acids under mild reaction conditions with easy separation and reuse of the catalyst.
It is observed that a novel water soluble transition metal complex provides an improved catalyst for the carbonylation of olefins, organic halides and alcohols to corresponding saturated carboxylic acids under biphasic conditions. The use of such a catalyst gives good yields of carboxylic acids under mild reaction conditions with easy separation and reuse of the catalyst.
Accordingly, an object of the present invention is to provide a process for preparation of carboxylic acids by carbonylation of corresponding olefins, organic halides and alcohols using novel water-soluble palladium complex catalysts under biphasic conditions.
It is another object of the invention to develop a process for the preparation of carboxylic acids by the carbonylation of corresponding olefins, organic halides and alcohols which provides improved yield of the product.
It is another object of the invention to develop a process for the preparation of carboxylic acids by the carbonylation of corresponding olefins, organic halides and alcohols which has improved reaction rates and good regioselectivity to 2-aryl propionic acids.
Another object of the invention is to develop a process for the preparation of carboxylic acids by the carbonylation of corresponding olefins, organic halides and alcohols which provides easy separation and recycle of the catalyst.
Another object of the invention is to develop a simple and efficient process for preparation of carboxylic acids by carbonylation of corresponding olefins, organic halides and alcohols.
Accordingly, the present invention provides a process for the preparation of a carboxylic acid of the general formula III, 
wherein R1 is aryl, substituted aryl, naphthyl, substituted naphthyl or alkyl, R2, R3, R4 and R5 are independently hydrogen or alkyl, said process comprising reacting the corresponding olefin of formula I or the corresponding organic halide or alcohol of the formula II, 
wherein R1 is selected from the group consisting of aryl, substituted aryl, naphthyl, substituted naphthyl or alkyl, R2, R3, R4 and R5 are independently hydrogen or alkyl and X is a halogen atom or a xe2x80x94OH group, in the presence or absence of an organic solvent, a protonic acid, and/or an alkali metal halide, using a novel water soluble palladium complex catalyst of general formula IV 
wherein R1, R2 and R3 are substituent on the phosphine ligand and selected from the group consisting of alkyl, aryl, arylalkyl, an cycloaliphatic, at least one of which carries a sulfonic acid and salts thereof, X is aryl or alkyl sulfonato or aryl or alkyl carboxylate or formato or a halide, 
is an anionic chelating ligand containing a N donor and Oxe2x80x94 group, in degassed water with or without excess sulfonated phosphine, in carbon monoxide atmosphere under biphasic conditions, at a temperature ranging between 30 to 130xc2x0 C., for a period ranging between 0.3 to 24 hrs, at pressures ranging between 50 to 1500 psig, cooling the reaction mixture to ambient temperature, flushing the reaction vessel with inert gas, separating the aqueous catalyst phase and removing the organic solvent, and isolating the compound of formula III from the organic layer.
In one embodiment of the invention, the anionic chelating ligand is selected from the group consisting of 8-hydroxyquinoline, 2-hydroxypyridine, (2-hydroxyethyl)pyridine, pyridil-2-, pyrezyl-2, piperidyl-2-, piperzyl-2-, quinolyl-2-, isoquinolyl-1- and isoquinolyl-2-carboxylates, particularly pyridyl-2-carboxylate, piperidyl-2-carboxylate and 8-hydroxyquinoline.
In another embodiment the sulfonated phosphorous ligand used is a sulfonated mono phosphine.
In a further embodiment of the invention, the sulfonated mono phosphine is selected from the group consisting of tris(sodium-3-sulfonatophenyl)phosphine (TPPTS), phenylbis (sodium-3-sulfonatophenyl) phosphine (TPPDS), diphenyl(sodium-3-sulfonatophenyl) phosphine (TPPMS), methylbis(3-sulfonatophenyl)phosphine, cyclohexylbis (sodium-3-sulfonatophenyl)phosphine, isopropylbis (sodium-3-sulfonatophenyl) phosphine, dimethyl (sodium-3-sulfonatophenyl) phosphine, and dicyclohexyl(3-sulfonatophenyl)phosphine.
In another embodiment the amount of sulfonated phosphine ligand used per gram mole of palladium may be 1-10 mole , preferably 2-3 moles.
In yet another embodiment the halide source if used for the carbonylation reaction may be any of the halide salts such lithium chloride, sodium chloride, potassium chloride, lithium iodide, lithium bromide, sodium bromide, sodium iodide, potassium bromide, potassium iodide, tetrabutyl ammonium chloride, tetrabutyl ammonium bromide and tetrabutyl ammonium iodide or hydro halic acids such as hydrochloric acid, hydrobromic acid and hydroiodic acid.
In another embodiment the protonic acid used may be any of the hydro halic acids such as hydrochloric acid, hydrobromic acid and hydro iodic acid or other protonic acids such as paratoluenesulfonic acid, methanesulfonic acid, triflouromethanesulfonic acid, formic acid, oxalic acid, acetic acid and trifluoroacetic acid.
In yet another embodiment the organic solvent for the carbonylation reaction if used may be benzene, toluene, xylenes, petroleum ether, hexane, heptane, decane, methyl ethyl ketone, chloroform, dichloromethane or diethyl ether.
In another embodiment the concentration of catalyst may be one mole of catalyst for every 50 to 50000 moles of substrate preferably 1 mole of catalyst for every 100 to 10000 moles of substrate and more preferably one mole of catalyst for every 150 to 5000 moles of substrate.
In still another embodiment the amount of halide source per gram mole of catalyst may be in the range of 5 to 500 moles preferably 20 to 300 moles, and more preferably 50 to 200 moles.
In another embodiment the amount of acid source per gram mole of catalyst may be in the range of 5 to 500 moles, preferably 20 to 300 moles, and more preferably 50 to 150 moles.
In a feature of the invention, the reaction can be conveniently carried out in a stirred reactor with the improved catalyst employed with a suitable solvent in presence of carbon monoxide.
The improved process of the present invention is described herein below with examples, which are illustrative only and should not be construed to limit the scope of the present invention in any manner.